The present invention pertains generally to high-temperature materials and in particular to phthalonitrile monomers and polymers therefrom.
Phthalonitrile polymers constitute a recent and important class of high-temperature materials, having a wide range of uses, such as composite matrices, adhesives, sealants, and even semiconductors. These polymers are prepared from phthalonitriles in which the linking group between the two ortho dinitrile groups separates the dinitrile groups enough to permit polymerization. Presently several bridging groups are known; examples include aliphatic and unsaturated groups, aromatic groups, aliphatic and aromatic diamide groups, and aliphatic and aromatic ether, sulfone and ketone groups.
The chemical and physical properties of the polymers depend primarily on the bridging groups. The groups providing the best properties are those with aromatic, polar and flexible moieties, especially the --O--.phi.--C.sub.3 H.sub.6 --.phi.--O-- group of U.S. Pat. No. 4,223,123 by Keller et al., the --O--.phi.--SO.sub.2 --.phi.--O-- and --O--.phi.--(C.dbd.O)--.phi.--O-- groups of U.S. Pat. No. 4,234,712 by Keller et al., and the --O--C.sub.n H.sub.2n --O-- group of U.S. Pat. No. 4,226,801 by Keller et al. These polymers have exceptional thermal and oxidative stability, low water absorptivity, high strength, good dimensional integrity, and strong adhesion. The aromatic moieties provide the high mechanical strength and modulus and the polar moieties provide the excellent adhesive properties.
Although these polymers have flexible moieties in the linking group, the toughness of these polymers is not high because of the shortness of the bridging group. It is believed that bridging groups from compounds, such as those described in Ahmed et al., The Properties of Some Poly(arylene ether sulfone), J. Appl. Poly. Sci., 25, p. 821-8(1980), should provide extremely tough polymers with all of the other advantageous properties of the aforementioned polymers. Also these polymers should be more easily processed because a phthalonitrile monomer with a short bridging chain is difficult to polymerized. Unfortunately no synthesis is known which can control the degree of polymerization of these polysulfones or link this type of compound with phthalonitrile groups. Thus the problem remains in devising a synthetic method for linking aromatic nuclei with sufficient versatility and freedom from side reactions to effect the synthesis of phthalonitriles with a wide range of molecular-weights.